memcg: fix NULL pointer dereference in __mem_cgroup_usage_unregister_event
[muen/linux.git] / mm / memcontrol.c
index 2058b8d..50492aa 100644 (file)
@@ -4027,7 +4027,7 @@ static void __mem_cgroup_usage_unregister_event(struct mem_cgroup *memcg,
        struct mem_cgroup_thresholds *thresholds;
        struct mem_cgroup_threshold_ary *new;
        unsigned long usage;
-       int i, j, size;
+       int i, j, size, entries;
 
        mutex_lock(&memcg->thresholds_lock);
 
@@ -4047,14 +4047,20 @@ static void __mem_cgroup_usage_unregister_event(struct mem_cgroup *memcg,
        __mem_cgroup_threshold(memcg, type == _MEMSWAP);
 
        /* Calculate new number of threshold */
-       size = 0;
+       size = entries = 0;
        for (i = 0; i < thresholds->primary->size; i++) {
                if (thresholds->primary->entries[i].eventfd != eventfd)
                        size++;
+               else
+                       entries++;
        }
 
        new = thresholds->spare;
 
+       /* If no items related to eventfd have been cleared, nothing to do */
+       if (!entries)
+               goto unlock;
+
        /* Set thresholds array to NULL if we don't have thresholds */
        if (!size) {
                kfree(new);